In an engine, a portion of heat generated from a cylinder, or combustion chamber, is absorbed by a cylinder head, a cylinder block, an intake/exhaust valve, a piston, and so on. When these components are heated to an excessively high temperature, thermal deformation or lubrication deficiency due to a damage of an oil film formed over an inner wall of the cylinder block occurs, thereby generating thermal defects.
Thermal defects of the engine may generate abnormal combustion such as defective combustion and knocking such that the engine suffers damage such as erosion of the piston. On the other hand, excessive cooling of the engine may lead to problems such as degradation of fuel economy caused by low thermal efficiency, cylinder wear at low temperature, and so on. Thus, it is advantageous to properly control the temperature of a coolant C (see FIG. 1) flowing between an outer wall and an inner wall in the cylinder block.
As shown in FIG. 1, in a conventional case, a cylinder liner 10 made of cast iron is provided along an inner wall of a cylinder block in order to enhance thermal efficiency through prevention of heat loss. In this case, however, lightness of an associated vehicle may not be achieved due to weight of the cylinder liner 10. Although an upper portion of the cylinder block is cooled to prevent abnormal combustion such as knocking, the entire inner wall of the cylinder block is surrounded by the cylinder liner 10 made of cast iron such that it is difficult to solve the above-mentioned problems.
The matters disclosed in this section are merely for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgment or any form of suggestion that the matters from the related art already known to a person skilled in the art.